1. Field
The present disclosure relates generally to aircraft and in particular, to a method and apparatus for determining and validating the air mass state of an aircraft.
2. Background
Modern commercial aircraft have increasing demands for availability and integrity of air data. Air data describes the air mass state of an aircraft around the aircraft during flight. This air data is used by pilots and on-board systems to make operational decisions and control actions regarding an aircraft. This air data may include, for example, pitot or total pressure, static pressure, angle of attack, angle of sideslip, and other suitable air data. Conventional sensors used to measure this type of data may be adversely affected by environmental conditions or other conditions or events.
For example, ice or other foreign materials may prevent an accurate measurement of pressure by a pitot tube used to measure total pressure. This type of tube is a pressure measurement instrument used to measure fluid velocity. The measured pressure is the stagnation pressure of the air which is also referred to as total pressure. This measurement, together with static pressure measurements measured using static port sensors on the side of the fuselage, may be used to identify the impact pressure.
The impact pressure may then be used to calculate an airspeed of the aircraft. A pitot tube may become clogged with ice or other foreign materials, resulting in an inaccurate measurement. This type of an inaccurate measurement may result in an inaccurate identification of airspeed for an aircraft.
These types of situations may be avoided through various preventative mechanisms. For example, redundant sensors may be used as well as heating elements to reduce environmental effects. With fly-by-wire aircraft becoming more common, even higher demands are placed on obtaining trustworthy data from air data sensors, because this air data information is used for full-time control augmentation. Closed-loop sideslip control and envelope protection are examples of control augmentations for a fly-by-wire aircraft that rely on air data.
Historically, cross instrument comparators have been implemented to draw the attention of a pilot to the left and right differences of airspeed and altitude. These comparators may be used by a pilot to decide which instrument may be faulty and select only the sensors from which accurate data is being obtained. Other currently used mechanisms provide a voting process in which trusted data is furnished to pilots and various systems on the aircraft. This type of voting system automatically removes data from sources that are determined to be faulty.
It would be advantageous to have an improved method and apparatus for determining and validating air data for an aircraft and addressing the problems as discussed above.